The present invention relates to a storage remote copying method in an information processing system in which a plurality of storages are connected via network, and in particular, it relates to a technique for data transfer and disaster recovery.
A system failure in the information processing system including a storage device, due to power failure, fire disaster, earthquake and the like, may cause a temporary halt of operation, data loss and the like. In order to avoid such a situation, a similar information processing system is provided at a remote place where there is no influence from such a fire disaster, earth quake and the like. Then, write data is transferred to that system so that a copy can be prepared. For implementing such a configuration as described above, there exists a technique for transferring data to make a copy, utilizing a network device (hereinafter, referred to as “remote copy”).
“Remote copy” means to transfer data to a system including a storage device at a remote location. Accordingly, even when a system at one site goes down due to a disaster, the system can be recovered by data backup, operation take-over and the like at the remote location.
There are two types of “remote copy”, i.e., synchronous remote copy and asynchronous remote copy. Specifically, in the synchronous remote copy, in response to a write request from a computer of an information processing system, a storage device of the information processing system completes data transfer to a remote storage, and thereafter gives a response to the write request from the computer. Therefore, in the synchronous remote copy, there is little possibility of data loss due to a system failure, and consistency in data transfer is guaranteed. However, in the case of delay in lines between the storages, I/O delay between the computer and the storage may occur.
On the other hand, in the asynchronous remote copy, upon receipt of writing from the computer, the storage device makes a response at the timing of writing into the storage in itself and does not wait for a response from the data transfer destination at a remote location. With this configuration, I/O performance delay between the computer and the storage device rarely occurs even if a distance between the storage devices is long, the possibility of data loss occurrence becomes higher, comparing to the synchronous remote copy, and data order is not guaranteed.
As for the guarantee in data consistency in the asynchronous remote copy, there is disclosed a method that additional information is attached to the write data, and based on the additional information, sorting of data is carried out in the system at the remote location to guarantee the data consistency (see the Japanese Patent Laid-open Publication No. 2002-149499, hereinafter referred to as “Patent Document 1”).